US Patent 7458607 Airbag and airbag apparatus

An inner part of an airbag is partitioned into a first chamber and a second chamber by first and second inner panels. In a rear panel, a venthole for allowing the second chamber to communicate with an outer part of the airbag is provided. A lid member covers the venthole and is combined with the rear panel in a vicinity of the venthole by a tear seam. The lid member is connected to the second inner panel by a tether. At an initial stage of airbag expansion, the venthole is covered by the lid member. When the airbag is expanded more than a predetermined amount, the lid member is stretched by the second inner panel via the tether, and released from the venthole so as to open the venthole. The airbag facilitates prompt deployment without a loss in shock-absorbing characteristics.